The invention relates to a manually actuated, preferably exclusively manually actuated and mobile, strapping unit.
Strapping units of this type are frequently provided for mobile use so that a user can wrap a steel strap around a packaged item in any desired location. A generic type of these strapping units typicallarly has a sealing device which produces a connection of two layers of the steel strap by means of multiple notchings, without using an additional sealing element, such as, for example a lead seal. For this type of strapping unit it is also typical for both the strap tension and the formation of a seal to be produced manually without the assistance of outside energy, in particular electric or hydraulic energy. For this purpose, the operator of a strapping unit according to the generic type has only to provide his own muscular power. However, the invention is also suitable for another generic type of strapping unit, in which either a sealing element, such as the already mentioned lead seal, or auxiliary energy, such as, for example, electric energy, is used for producing a welding connection in the case of plastic straps. However, a common feature of the generic types of strapping unit is that a tensioning wheel is driven by a manually actuated tensioning lever.
In order to apply a tension to the strap loop, the tensioning wheel has to be caused to rotate by means of the tensioning lever. By means of a frictional lock between the tensioning wheel and the strap layer in contact with it, the strap layer can be moved in the direction of a supply reel of the strap, as a result of which the strap loop becomes smaller and the strap tension consequently becomes greater. Conventionally, the tensioning lever can be moved only over a limited angular range, for example 120xc2x0, in one direction of rotation. However, the tensioning-wheel rotation associated therewith does not suffice in order to obtain a sufficient strap tension. For this reason, it is necessary to actuate the tensioning lever a number of times by moving the latter to and fro in an oscillating movement between two end positions of rotation. So that the tensioning wheel is not moved back again here counter to the tensioning direction of the strap, the tensioning lever is connected to the tensioning wheel via a coupling.
In the case of previously known strapping units of the type mentioned at the beginning, the coupling is designed here as a ratchet having a spring-loaded catch which engages radially in correspondingly shaped gaps of a wheel. Such a coupling of a tensioning drive is realized, for example, in the unit from the same applicant which is sold under the designation CM 14.
What may not be satisfactory, however, with this previously known solution is that, in particular, the catch has to be of relatively solid design on account of the high forces and torques which are in action, and this coupling therefore requires a large amount of space and involves a high weight.
The invention is therefore based on the object of proposing a coupling for an operative connection between the tensioning lever and the tensioning wheel, which coupling is designed more favorably in terms of the structure in comparison with catch-type couplings.
This object is achieved according to the invention in the case of a strapping unit of the type mentioned at the beginning by an axial coupling being provided in a force flux from the tensioning lever to the tensioning wheel. Within the context of the present invention, axial couplingsxe2x80x94or else axial surface couplingsxe2x80x94can be understood to be those couplings in which one coupling part has, as constituent part, an axial surface in the region of the tensioning shaft, i.e. a surface or a plane of the surface through which the tensioning axis runs, and this axial surface or plane can be brought into operative connection with another coupling part to be coupled on. In a structurally simple and preferred embodiment, the axial surface can be one end side of the tensioning shaft itself. However, the axial surface can also surround the tensioning shaft. A second axial surface assigned to the tensioning lever can then enter into and come out of operative connection with the first one, in order to complete or cancel a force flux between the tensioning lever and the tensioning wheel.
It has proven particularly preferable if a plurality of segments which can be brought into and out of engagement are present in each case on the two axial surfaces. Segments of this type can each have one flank surface which is brought to bear against a flank surface of a segment of the respectively other coupling part. The positive lock arising by this means then leads during a movement of the tensioning lever in a predetermined direction of rotation to a rotational movement of the tensioning wheel. The flank surfaces should preferably be aligned parallel and radially with respect to the tensioning axis. Since a plurality of flank surfaces are simultaneously in engagement with one another, it is possible to transmit a high torque in a small space. The size of the transmittable torque can be increased or reduced in a specific manner by increasing the sum of the total area of the flank surfaces.
In order for the tensioning lever to be decoupled from the tensioning shaft in a direction of rotation opposed to the direction of rotation assigned to the positive lock, it may be expedient to design the segments in such a manner that they can slide on one another. In order to achieve this, one structural solution may consist in providing the segments with surfaces which rise in a ramp-like manner with respect to the axial surface.
In a further preferred embodiment of the invention, the segments of both axial surfaces can be designed as a Hirth-type serration. The geometrically simple Hirth-type serration has all of the above-described advantages and can be manufactured comparatively simply.
Further preferred refinements of the invention emerge from the dependent claims, the description and the drawing.